Urea uptake and nitrogen mobilization by apple leaves in relation to tree nitrogen status in autumn
The research paper investigates the relationship between urea uptake and nitrogen (N) mobilization in apple leaves, particularly focusing on how these processes are influenced by the nitrogen status of the trees during autumn. The study was conducted using bench-grafted Fuji/M.26 apple trees that were fertigated with varying nitrogen concentrations (0, 2.5, 5, 7.5, 10, 15, or 20 mM) from June 30 to September 1. In mid-October, the trees were divided into three groups: one for assessing background nitrogen status, one for applying a 3% N-enriched urea solution, and a control group.
The findings revealed that nitrogen fertigation led to a significant variation in tree nitrogen status, as indicated by leaf nitrogen content ranging from 1.3 to 3.5 g m² in autumn. The study found that the percentage of nitrogen partitioned into the foliage increased linearly with leaf nitrogen content up to 2.2 g m², after which it plateaued at 50-55%. Conversely, nitrogen uptake and mobilization per unit leaf area decreased with increasing leaf nitrogen content. For control trees, nitrogen mobilization per unit leaf area increased with leaf nitrogen up to 3 g m², then leveled off, while the percentage of nitrogen mobilization remained around 60% until leaf nitrogen reached 3 g m², after which it declined.
The application of foliar N-urea reduced the mobilization of endogenous leaf nitrogen, regardless of the tree's nitrogen status. Overall, the study concluded that trees with low nitrogen status are more efficient in absorbing and mobilizing nitrogen from foliar urea compared to those with high nitrogen status, and that more nitrogen from foliar urea is allocated to the root systems of low nitrogen trees.
This research paper is significant in the field of horticultural science and plant physiology as it provides insights into nitrogen management in apple trees, which is crucial for optimizing growth and fruit production. The findings contribute to ongoing discussions about nutrient management strategies in fruit cultivation, particularly in relation to nitrogen fertilization practices. By demonstrating the differential responses of trees based on their nitrogen status, the study offers practical implications for growers aiming to enhance nitrogen use efficiency and improve overall tree health. The research also highlights the importance of understanding the physiological mechanisms behind nutrient uptake and mobilization, which can inform future studies and agricultural practices.
